(not applicable)
1. Field of the Invention
The present invention relates to reactors for the processing of gaseous media and, more specifically, to reactors for removing nitrogenous and carbonaceous combustion products from the exhaust emissions from internal combustion engines.
2. Description of the Related Art Including Information Disclosed Under 37 CFR. 1.97 and 1.98.
Reactors for removing noxious substances from the exhaust gases from internal combustion engines conventionally have a circular, or at most elliptical cross-section. Examples of such reactors are shown in our patent GB 2,274,412. Other examples are shown in EPO 0 010 384; U.S. Pat. Nos. 4,485,622; 4,427,418 and 4,276,066; EP 0 244 061; EPO 112 634 and EPO 132 166.
Circular cross-section reactors are satisfactory for use with smaller sizes of engines where the volume flow rate of exhaust gas is limited, but for larger engines, such as those of commercial vehicles, the diameter of the reactor becomes excessive, particularly in reactors of the type in which there is a hollow cylindrical bed of active material and the exhaust gases to be treated are caused to flow initially axially into a space between the outside of the bed of active material and the wall of the reactor before being diverted to flow radially through the bed of active material.
Specifications GB 1,296,874, GB 1,354,752, WO 94/12777 and U.S. Pat. No. 5,593,645 disclose reactors for the catalytic treatment of exhaust gases from internal combustion engines. The reactors disclosed in these specifications include a pair of planar gas permeable reactor beds which are disposed symmetrically about the median planes of the reactors. The exhaust gases are admitted to the upstream end of the gap between the reactor beds and pass outwardly therethrough. However, again, the amount of exhaust gases which can be admitted to the gap between the reactor beds is limited by the practicable width of the reactor beds. Also, the rate of outward flow of the exhaust gases varies along the length of the reactor beds resulting in a similar variation in the treatment efficiency of the reactor beds.
It is an object of the present invention to provide a reactor for the processing of gaseous media which is more susceptible to scaling than those used hitherto and which provides for a higher overall treatment efficiency for the gaseous media.
According to the present invention there is provided a reactor for the processing of a gaseous medium, comprising a reactor chamber of rectangular cross-section, two planar reactor beds made of a gas permeable active material, the reactor beds being disposed symmetrically about a median plane of the reactor chamber with a gap therebetween and contained within an outer wall structure, the reactor chamber, the reactor beds and the outer wall structure defining a through gas flow path including the gap between the reactor beds, the reactor beds themselves and gas passages between the reactor beds and the reactor chamber, characterised in that the said wall structure includes a gas feed passage extending around at least a portion of the wall structure and adapted to feed incoming gaseous medium onto the reactor beds transversely of the original direction of flow of the gaseous medium.
Preferably the gas feed passage is adapted to feed incoming gaseous medium to the gap between the reactor beds, the gaseous medium flowing through the reactor beds and being collected from the outer surfaces thereof.
Preferably the two reactor beds are each contained between two perforated metal plates adapted to act as electrodes so that a potential can be applied to the reactor beds sufficient to initiate and maintain a plasma in the gaseous medium as it flows through the reactor beds.
Also there is provided a reactor for the plasma-assisted treatment of the exhaust emissions from internal combustion engines comprising, a reactor chamber of rectangular cross-section, two planar reactor beds made of a gas permeable material having a dielectric constant sufficient to enable a plasma to be excited and maintained in the exhaust gases as they pass through the reactor beds, each reactor bed having a pair of gas permeable electrodes by means of which a potential difference sufficient to excite the said plasma to be applied across the reactor beds characterised in that the reactor beds are disposed parallel to each other symmetrically about the median plane of the reactor chamber and that there is included around the peripheries of the reactor beds a wall structure made of an impervious heat resistant insulating material having a gas passage extending around at least a portion of the wall structure and adapted to admit the exhaust gases to the region between the reactor beds transversely of the original direction of flow of the exhaust gases entering the reactor chamber.